Actually it takes 3 sandwich size zip lock baggies. Fill the 1st one 1/4 to 1/3 full of water, push all the air out of it, seal it. Put in in another baggie,push all air out of it, seal it. flatten these out. Put these to inside another baggie, flatten out, push all air out,seal it Roll baggies...
I've never heard of anyone using a jar of water for a wiggler. So I can't tell you how it would compare to the consistancy of an egg. I can tell you how to make one out of baggies that works real well that I found on this site.